The second amendment is the most important because it's the one that lets us get the rest back if we need to.
What happens if things get so bad as to cause revolt, but there's nothing to revolt with because it was all taken away?
What happens when most of the people who have the guns merely shrug their shoulders when all the other rights are taken, because "hey, at least they're not taking our guns"?
There is no "most important" amendment. They're all equally important. You can't revolt even with guns if the First Amendment is taken, and you have no way of communicating with like-minded people, for example.
Excuse my pessimism, but all the cheerleading of the Patriot Act from the gun-owning crowd didn't exactly give me the warm and fuzzies over the last six years. What good are your guns if there's nothing left to defend with them...except your right to keep those guns?
As someone else pointed out, the Second is the only amendment that refers to tangible objects. I can hide my guns...I can't hide my freedom of speech, or my right to a jury trial.
But if a candidate doesn't support you on gun issues he/she is unlikely to be supportive of any other issue you feel strongly about.
There are a ton of candidates who agree with me on the gun issue, but whose beliefs are diametrically opposed to mine on every other important issue.
A candidate's position on guns tells you nothing about his position on freedom in general--it just tells you that he likes guns. Most people have a favorite Amendment or two, and they usually also have an amendment or two they'd like to see gone.